Insufficient dietary intakes and a variety of diseases are often associated with an increased risk of linear enamel hypoplasias (LEH) and other developmental defects of enamel (DDE). However, little is known about how the interaction between morbidity and nutritional intake affects the formation of DDEs, whether certain nutrients and morbidity events are most causative of DDEs (specificity), and the sensitivity of various types and degrees of DDEs to these common physiological perturbations. Thus, the purpose of this study is to collect and examine empirical data on the interrelationship of nutritional intake and morbidity in the development of enamel developmental defects. Specific aims are to: (a) evaluate the effect of macronutrient intake and morbidity separately and in combination, on the development of LEHs and others DDEs, (b) to assess whether qualitative aspects of morbidity diet (intake of micronutrients such as retinol and zinc), and nutritional status are specifically predictive of the formation of a different types and degrees of DDEs, (c) to compare the sensitivity of different teeth to developmental disruption due to variations in nutrition and disease, and (d) to model the etiology of DDE formation. As part of a interdisciplinary and multinational study of mild-to- moderate malnutrition, dietary, morbidity and supplemental data were obtained at frequent intervals in 1984-85 from a cohort of children from their 18th to 30th month (n = 124 from the Solis valley, Mexico; n = 154 from Kalama, Egypt). The proposed study involves a follow-up of these children. Permanent tooth DDEs will be recorded clinically, photographically and on dental casts. Data linkage and subsequent statistical analysis will focus on hypothesis testing and model building. Because the proposed study entails a longitudinal and prospective analysis of a cohort, it provides a unique opportunity to understand how nutritional intake and morbidity influence enamel development. These data may provide a better understanding of the etiology and interrelationship of DDES and, by extension, the requirements for normal enamel development. Ultimately, it is expected that LEH and other DDEs may help to evaluate the degree and consequences of early life developmental perturbations.